| Ill | |
| Image Alt: | The Ill near Gisingen (district of Feldkirch). |
| Subdivision Type1: | Country |
| Subdivision Name1: | Austria |
| Subdivision Type2: | State |
| Subdivision Name2: | Vorarlberg |
| Source1 Coordinates: | 46.8692°N 10.1089°W |
| Mouth Coordinates: | 47.2992°N 9.5586°W |
| Length: | 72km (45miles) |
| Source1 Elevation: | 2240m (7,350feet) |
| Mouth Elevation: | 1811m (5,942feet) |
The Ill (all capitals: ILL) is a 72adj=midNaNadj=mid tributary of the Rhine in the western Austrian state of Vorarlberg.
It flows from the northern slopes of the Silvretta mountain range and then runs north-west through Vorarlberg. The Ill passes through the Montafon and valleys and the town Feldkirch. It joins the river Rhine a few kilometers northwest of Feldkirch ("Illspitz"), at the border with Switzerland. The Ill has several dams with hydroelectric power stations.